Fix memory leak in ExceptionWrapper

[mvorisek]

Currently ExceptionWrapper stores the original exception forever and prevents it to be GCed.

This is causing not only memory to grow/leak, but also if the original exception has a reference to an object, the object is not released as well. Such scenario is not uncommon, as exception stack trace/frame can contain object arguments.

In consequence when the unreleased object is a some limited resource like DB connection, with a lot of wrapped/unreleased exceptions, the resource can be exhausted by a few failing tests making the other tests fail because of them.

This fix maintains the shallow backtrace as WeakReference property is not expanded during backtrace dump.

No BC break introduced.

[codecov[bot]]

Codecov Report

Merging #5012 (bd1a437) into 9.5 (8885568) will decrease coverage by 0.02%. The diff coverage is 42.85%.

@@             Coverage Diff              @@
##                9.5    #5012      +/-   ##
============================================
- Coverage     83.82%   83.79%   -0.03%     
- Complexity     4615     4618       +3     
============================================
  Files           272      272              
  Lines         11470    11474       +4     
============================================
  Hits           9615     9615              
- Misses         1855     1859       +4     

Impacted Files	Coverage Δ
src/Framework/ExceptionWrapper.php	89.18% <42.85%> (-10.82%)	:arrow_down:

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[mvorisek]

I have updated the PR description to understand the real issue better. Please merge this fix into at least phpunit 9.5.

For next major release, is there any reason to not drop ExceptionWrapper completely?

[sebastianbergmann]

For next major release, is there any reason to not drop ExceptionWrapper completely?

The ExceptionWrapper has been removed in the main branch.

[mvorisek]

The ExceptionWrapper has been removed in the main branch.

Thank you ❤️

To fix the memory leaks in phpunit 9.5, can this PR be merged into 9.5.x branch? No BC break should be involved.